1. Field of the Invention
This invention relates to communications systems and methods for broadcasting television and multimedia content to user terminals located within desired coverage areas, and also relates to user terminals and receiving devices for receiving content transmitted via satellite communications networks.
2. Background Information
A satellite is a sophisticated electronic communications relay station orbiting the Earth. Earth stations (which are also known as parabolic dishes) transmit signals to a satellite in orbit, which is called “uplinking.” Satellites receive this signal, amplify it, shift it to a different (usually lower) frequency and then feed the outgoing signal into an on-board satellite antenna, where the signal is focused into a beam and sent back to Earth. The act of sending the signal back to earth is known as “downlinking.” The spacecraft electronic hardware that receives the uplinked signal, amplifies it and sends it back to Earth is called a “transponder.”
Satellites are used around the world in a variety of entertainment and telecommunications applications. Most commercial satellite communications take place in L, C, and Ku band microwave frequencies. Satellites have distinct advantages over terrestrial networks for wide area broadcasting, multi-point-to-point communications and for broadcasting in rural or geographically disadvantaged areas. As an example, satellite data terminals, known as VSATs (Very Small Aperture Terminals), provide credit and debit card transaction network communications from retail stores, gas stations, and banks at hundreds of thousands of locations around the globe. New locations can be provisioned and decommissioned quickly and at a low cost, compared to the time and cost of connecting locations by other methods. As another example, mobile voice networking via satellites enables individuals (such as reporters or natural resource engineers) to utilize portable computers or handheld satellite phones to report from third-world countries or low-density population rural areas.
Perhaps the most commonly associated application of satellite communications is for point-to-multipoint television distribution. Across the world, it is likely that satellites are used for at least one segment of television distribution, wherever it is watched. Broadcast networks supply content to local affiliates and cable television stations provide content to local cable providers (headend systems) via satellite. As the programming content (or, perhaps, syndication programming and advertising) is received over satellite, it is then broadcast to consumers by transmission from the local affiliate or the local cable company. For example, television programming from a single network hub can be delivered to numerous ground-based broadcasters or cable operators by a geosynchronous satellite. Such broadcast applications take full advantage of the wide area coverage provided by geosynchronous satellites.
As shown in FIG. 1, the information that is to be broadcast to a number of receivers within the field of view of the satellite is delivered to a hub earth station 1, which then uplinks the information to the satellite 2. The satellite then relays the information to user terminals 3 located within a broad coverage footprint 4 on the earth. For example, television programming from a single uplink earth station can be delivered to a national network of terrestrial TV broadcast affiliates by a geosynchronous satellite. In excess of 10,000 US cable television headends also receive the majority of their programming via satellite. Such broadcast applications take full advantage of the wide area coverage provided by geosynchronous satellites. Every television station in the United States owns and operates at least one television receive-only (TVRO) satellite terminal, and many stations own uplink terminals to deliver news feeds via satellite. Television programming is most commonly distributed using the C band (6/4 GHz) of frequencies.
The cable/satellite connection described above was the first widespread use of satellite technology and one that greatly influenced the ultimate direction of satellite technology. A typical cable system head-end in the United States will continuously receive up to 70 satellite-delivered video channels from a handful of Fixed Satellite Services (FSS) satellites in the Western North American geostationary arc known as the “cable neighborhood.” Much of today's cable subscriber programming is transmitted in an analog format, using the satellite equivalent of a conventional 6 MHz TV channel. FSS satellites generally comprise of 24 channels, each 36 MHz wide (generally equivalent in capacity to a 6 MHz terrestrial television signal). Individual cable head-ends point a TVRO earth station at each satellite in the cable neighborhood to receive the analog and digital feeds from the content providers. Integrated Receiver Decoders (IRDs) are used to receive, demodulate, decrypt, and decode the individual programs. The demodulated (baseband) signals are then remodulated according to 6 MHz NTSC standards onto a cable TV frequency plan and combined with local off-air signals and cable modem data to form the broadband service that is amplified and relayed along a coaxial cable plant to the home subscriber.
The later decades of the twentieth century ushered in the advent of the latest innovation in satellite television distribution: digital multi-channel television via Direct Broadcast Satellite (DBS). This has garnered over 30 million household subscribers worldwide, thanks to free-flowing content, protected spectrum allocation, powerful satellite designs, low cost set top box technology, and a global regulatory environment that favors facilities-based multi-channel video competition. Examples of direct-to-home video distribution systems include the General Motors/Hughes Electronics DIRECTV system and the EchoStar DISH system. In such systems, the video signals are digitally encoded/formatted at the uplink or at a local off-air collection point using a compression/transport standard developed by the Motion Picture Experts Group (MPEG-2, ISO/IEC 13818-1). The signals are then encrypted and modulated to satellite transport specifications, usually those given in Digital Video Broadcasting (DVB-S) standards. The MPEG-2 signals are combined with an integrated Electronic Program Guide (EPG) at a single headend (the DTH broadcast center) that serves the entire United States. Instead of adding local signals at each headend, as in cable TV distribution, satellite DTH service providers collect the off-air signals at a local point-of presence (PoP) and backhaul them to the national broadcast center for transmission to the subscriber.
Most DTH service providers utilize high-power Ku band (12/17 GHz) satellites using the International Telecommunications Union Broadcasting Satellite Services (BSS) channel plan. Under the BSS plan, each orbital position is assigned 16 frequencies on two polarizations, thereby providing 32 channels. The 32 channels of approximately 27 MHz each can deliver between 200 and 300 digital video channels to the Continental United States (CONUS) and, with spot beam technology (described below in further detail), hundreds of local television channels into the smaller areas served by the spot beams.
Various schemes for direct-to-home broadcasting real-time and non-real-time television and multimedia content are known. One such technique, described by DVB-S (EN 300 421—Framing structure, channel coding and modulation for 11/12 GHz satellite services) is used throughout the world to broadcast in Ku-band BSS and FSS frequencies. Another method is a proprietary (but similar) technique used at DIRECTV. Both of these methods send real-time television and multimedia content using a traditional 32 or 24 frequency transponder plan. Although high-speed, full transponder data transmission is stipulated in both formats, the broadcaster operator does not transmit television programming in faster than real-time. These systems suffer from bandwidth limitations and the need for more efficient coding.
The fundamental unit of a satellite is a “transponder,” which refers to the Radio Frequency (RF) repeater described above within a satellite communications payload. A transponder translates the frequency of the uplink signal to a specified downlink frequency. The traditional transponder bandwidth of 36 MHz was chosen in 1965 for the first commercial satellite, “Early Bird,” to accommodate FM modulation of the 6 MHz television signal waveform. Each transponder was capable of receiving and retransmitting a single analog television signal. This became the fundamental building block of commercial satellite architecture.
The development of more powerful rockets in the 1960's enabled larger satellites to be built and launched to geosynchronous orbit. As rockets and satellites grew more incrementally more powerful, the gains were allocated to incrementally larger numbers of transponders. In some cases, higher power was used to reduce the transponder bandwidth to 27 MHz, which is sufficient for transmission of a single television signal fed with more power.
The 36/27 MHz transponder thus became not only a basic building block of satellites, but also the basic unit of satellite commerce. Most commercial satellites were, and still are, designed, built and launched by enterprises that offer short and long term transponder leases to other enterprises, such as television stations and networks. A company wishing to broadcast a single analog television channel leases a single transponder that covers an area into which the company wishes to transmit its programming. If the company is a cable television network, it will usually prefer a satellite that carries many other cable television networks, since the signal can be more easily received by cable headends that already receive other services from that satellite. Instead of building a new receiving dish, the cable headend will simply have to add a new tuner to receive the additional transponder frequency. Although a single satellite receiving dish can collect all signals transmitted by a single satellite, a separate tuner is needed for each transponder. Twenty four tuners, but only one dish, is needed to receive simultaneously all of the signals from a 24 transponder satellite. A single tuner can be adapted to be capable of tuning among all 24 transponders, but can only receive one transponder at a time.
The need for multiple tuners is a consequence of the division of satellite capacity into multiple transponders. The burden of this constraint was relatively minor when most transmissions were analog and most satellite television transmissions were directed to commercial cable headends or broadcast stations with sophisticated plants and full time engineering staffs. The cost of adding a tuner to a cable headend serving hundreds or thousands of homes was nominal.
However, more and more satellite television transmissions—including those of DBS providers—are intended for receipt by consumers directly. The need for a separate tuner for each transponder received simultaneously has been a disadvantage for DBS providers, as it has driven up the cost of provisioning their customers to view different channels, at the same time, on different television sets, or to watch one channel while recording another.
Even with four or more tuners, DBS customers can simultaneously access only a small fraction of the total programming offered by a DBS provider, which may be using 40 or more transponders. This limitation is not fully appreciated today, since the overwhelming majority of television viewing is ephemeral or “real-time”—that is, the programming is viewed simultaneously with its transmission. Since there is a practical limit to the number of television channels a typical household can use at any one time, two, four, or six tuners will accommodate the requirements of most subscribers.
Cable television systems also have grown in an incremental way, with the basic unit still based on a single analog television channel.
In a world limited to “real-time” television usage, the incremental growth of both transmission and reception capacity through the addition of analog-channel equivalents on the transmission end, and additional tuners on the reception end, masks the inherent limitations of the current state of the art. The availability of personal video recorders (“PVRs”) will change the way in which people use television and will expose the underlying weakness of the incremental approach used by all current generation television delivery systems. PVRs continuously filter all available programming and then select and record programming on digital storage media for later use. The programming is selected based on user-defined profiles and preferences, wholly without regard to the source of the programming or the time of the broadcast. Because the programming may be watched at the leisure of the viewer, rather than at the time broadcast, the practical limit on the number of channels a consumer may wish to access (for recording or viewing) simultaneously is much higher than it is in a household that relies primarily on synchronous viewing, with occasional recording to videotape or use of picture-in-picture. It is not only conceivable, but likely, that a household 5 years hence may wish to access a dozen or more programs simultaneously. One television may be tuned to two sports broadcasts (one with picture in picture) while a third game is being recorded. Another television may be tuned to a high definition movie, while a third is employed for high-bandwidth full motion video gaming. At the same time, one or more PVRs may be recording six or more programs being broadcast simultaneously that happen to meet the profiles set by four or more people in the household. A time overlap of even one minute between two programs could preclude the recording of both, if the system limits the number of programs that can be simultaneously accessed.
The limits of current systems are clear. Unless a DBS receiving user terminal is equipped with 32 tuners, the user is limited to receiving only a small fraction of the content that is being transmitted at any one time. As noted, most satellite and digital cable set-top boxes can tune only to one or two “channels” simultaneously. The single or dual tuner design is a workable limitation if each television set has its own dedicated set-top box (STB). However, for a feature such as “picture-in-picture,” a second tuner is necessary. If a user wishes to view a “picture-in-picture” TV on a first transponder and a standard-sized TV channel from a second transponder and simultaneously record another channel, a third tuner is required. Eventually, the economic model for transponders (and the 6 MHz “channels” architecture associated with cable) becomes overburdened by the need for expensive multi-tuner set-top technologies on every TV set.
The technical platforms of the existing high power DBS services in the United States were designed nearly 10 years ago. DirecTV-1, a Boeing 601 class satellite, was launched in December 1993 and DirecTV service began in June 1994. Technologies such as hard drive-based PVRs, advanced video on demand (VoD), and wireless home networking were not contemplated in the early DBS thinking. Software-based video decoding and other “future proofing” design elements also were not feasible in 1994 due to poor microprocessor power and expensive Random Access Memory (RAM). Although some of these state-of-the-art features have been layered on top of legacy DTH systems, the need for backward compatibility has limited the ultimate potential for such powerful technologies. The full benefits of a decade of hyper-growth of digital media technology can be realized only in a system that is designed from the start with those benefits in mind.
In summary, the use of transponders, which were designed around television's 6 MHz channels, have resulted in the development of a “transponder approach,” in which the available RF spectrum is divided into manageable channels, or transponders. Known satellite communications systems operating in a broadcast mode therefore suffer from limitations on the data rate format and methods at which information may be delivered to user terminals.
Known systems for delivering large bandwidth multimedia content to users at high data rates suffer from a number of other limitations as well. As an example, the Geocast system, developed by Geocast Network Systems, Inc., promised to deliver high quality real-time or non-real-time multimedia content to personal computer desktops or set-top boxes by using new digital television broadcast or satellite spectrum. In the satellite-based Geocast model, multimedia content was uplinked to a DBS or FSS satellite that in turn broadcast the content for receipt by users with specially designed receivers. The digital TV broadcast spectrum manifestation of the Geocast system used 12 megabits per second to a “GeoBox” personal server which was equipped with a 40 GB hard drive and used a return path provided via the subscriber's dial-up or broadband ISP. The special receivers accepted live data feeds or could store content for later retrieval. The Geocast system therefore in principle allowed users to overcome the bandwidth limitations of conventional and last-mile Internet connections, for example. After users customized their receivers to their own interests, preferences, and demographics, the Geocast system matched content to individual receivers and delivered matched content to the receivers for real-time or later viewing.
While in principle the Geocast system combined the bandwidth and immediacy of broadcast television with the customization and control enabled by web browsing, the product suffered from several limitations. The bandwidth of the Geocast delivery service was limited by the bandwidth of the digital television frequency or the single satellite transponder bandwidth. Moreover, the Geocast system was focused on providing a variety of multimedia content, including audio, text, low-resolution video, and web pages. It is possible to provide a wide variety of such low-bandwidth media in a traditional television distribution channel, and this was the Geocast approach. Geocast did not disclose a method to make a large number of high bandwidth digital content accessible simultaneously, as it is being transmitted, by low cost consumer receiving equipment.
In summary, there is no satisfactory existing solution to the problem of delivering multimedia content in a broadcast mode to users at very high data rates. Accordingly, there is a need for an improved system and method for transmitting and receiving multimedia content.